1. Field of the Invention
This invention relates to a method and apparatus for slip-lining underground utility pipelines, both service lines and main lines. Slip-lining is a technique whereby a new plastic pipe is inserted into an existing pipeline, typically as a means for replacing the existing pipeline as the carrier, increasing the operational pressure of the pipeline, or improving the operating integrity of the pipeline.
2. Description of Related Art
To replace a leaking or deteriorated gas service line, utilities often insert a new plastic pipe through an existing pipe. The existing pipe is typically steel, but may be made of cast iron or any other material used for conduit. Generally, the pipe is replaced because of its age or operating condition, but other factors such as “preventative maintenance” or a need for changed operating conditions for which the existing pipe is not suited can warrant the replacement. The slip-line technique is used to reduce costs, risks, and inconveniences associated with trenching or boring in order to install the new pipe.
Slip-lining a gas service currently consists of initially excavating at each end of the pipe to be replaced, disconnecting the service from the main, disconnecting the service from the meter-set, then usually pushing either ½, ¾, or 1 inch plastic pipe, typically polyethylene (PE) pipe, through the “straight” section of existing pipe and connecting the plastic pipe back to the meter and main. Conventional slip-lining is not performed through pipes that have offsets. For those pipes having offsets, if slip-lining is practical at all, a hole is dug to remove the bend or offset so that the new plastic pipe can be inserted in both sections of straight pipe. Replacement of the main line may also be performed along with the service line replacements, using the insertion or slip-line method. To connect the new plastic service line to the newly inserted main line, a section of the old main line must be cut out to expose the new main line disposed within the old main line and to facilitate the attachment of the new plastic service to a new service connection fitting installed on top of the new main.